Flow measuring devices are frequently composed of at least one tube segment, in which openings must be machined, in order that sensors or transducers can have direct access to the measured medium. Examples for this include especially ultrasonic, inline, flow meters, and also thermal flow meters, vortex flow meters and magneto inductive flow meters. In order that these sensors or transducers are not supplementally exposed to the kinetic energy of the flow, they are mounted with a certain set back. For this, a branch is required, for example, a branch embodied as a nozzle. The nozzle must be able to withstand the process pressure, provide a mechanical connection of the sensor or transducer and be joined durably with the measuring tube.
A typical example of use of such nozzles is for ultrasonic, inline, flow measuring devices. Flow measuring devices are often applied in process and automation technology. They permit efficient determination of volume flow and/or mass flow in a pipeline.
Known ultrasonic, inline, flow measuring devices frequently work according to the travel-time difference principle. This is illustrated in FIG. 17. In such case, the different travel times of ultrasonic waves, especially ultrasonic pulses, or so-called bursts, are evaluated with and against the flow direction of the liquid. For this, ultrasonic pulses are sent at a certain angle to the tube axis both with as well as also counter to the flow. From the travel-time difference, the flow velocity and therewith in the case of known diameter of the pipeline section the volume flow can be determined.
The ultrasonic waves are produced, respectively received, with the assistance of so-called ultrasonic transducers. For this, such as shown in FIG. 17, in the case of so-called inline, ultrasonic, flow measuring devices 101, sensors 102 in the form of ultrasonic transducers are secured in the tube wall of the relevant measuring tube 103. The evaluation of the ascertained signals occurs in an evaluation unit 104.
The ultrasonic transducers are composed, normally, of an electromechanical transducer element, e.g. a piezoelectric element, and a coupling layer. The ultrasonic waves are produced in the electromechanical transducer element as acoustic signals and conveyed via the coupling layer to the tube wall and from there in the case of the inline variant led into the liquid.
The ultrasonic transducers are usually secured to the measuring tube by means of sensor nozzles distributed over the periphery of the measuring tube and inclined relative to the tube axis. The sensor nozzles must be welded in place manually. Thus, as a rule, manual welding methods are used as joining technology in this situation, because the nozzles are small in number, often tilted, partially poorly accessible, and must be placed on a round tube. Problematic, in such case, is that, as a result of the manual manufacture of the connection by means of conventional welding methods (typically metal protective gas welding, tungsten inert gas welding), the bonding of the branch is burdened with geometry varying over the periphery, residual stresses in the material and local hard spots in the material. Especially, the geometric variations of the welded seams can lead to the fact that local stress concentrations occur upon loading of the branch by an external bending moment. In the extreme case, such concentrations can lead to a component failure, especially in the case of a frequently oscillating loading.